Transparent electrostatic shield



Nov. 19, 1940. DE WlTT R. GODDARD 2,221,944

TRANSPARENT ELECTROSTATIC sm'w:

Filed Feb. 28, 1958 INVENTOR. D If? R. GODDARD ATTORNEY.

Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE De Witt Rugg Goddard,Riverhead, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application February 28, 1938, Serial No.193,206

3 (llaimsi This invention relates to a new and novel transparentelectrostatic shield which is particularly adapted to electricalcircuits employing photocells.

A feature of this invention is an electrostatic 5 shield which comprisesa solid member for retaining a liquid medium which acts as anelectrostatic shield through which light rays may pass.

For some purposes, it is desirable to have an electrostatic shieldtransparent to light In the case of a photocell being used to pick upthe light from the fluorescent screen of a cathode ray oscilloscope, thephotocell circuit is apt to be affected by the strong electric fieldpresent around the oscilloscope screen. Wire screen or mesh may be usedfor this purpose but the use of such a screen cuts oif part of the lightand also may introduce a high frequency tone or other undesirableeffects. The device I am about to describe provides an electrostaticshield without these limitations.

This invention will best be understood by referring to the accompanyingdrawing, in which:

Fig. 1 is a perspective view of the electrostatic shield of thisinvention; and

Fig. 2 is a perspective view of a shielded metallic container having aphotocell and having an aperture in the front portion thereof in whichis located the electrostatic shield of this invention, as shown in Fig.1.

Referring now in detail to the drawing, Fig. 1 shows a diagram of atransparent electrostatic shield. E and D are two glass plates separatedby a U-shaped block of solid material C. These plates are cemented tothis block so as to form a watertight cell F. A metallic strip B passesaround the inside of the U-shaped block 0 and in one extremity has aperforation A. The cell F is filled with a conducting solution ofsulphuric acid, sodium chloride, calcium chloride, etc. A

solution of any of these substances is essentially transparent tovisible light and yet is a good conductor of electricity. The metallicstrip B should be of a metal not aifected by the solution used. Itspurpose is to make an electrical contact to the electrolyte. The hole Ais to provide a connecting means for grounding this strip.

Fig. 2 shows a copper box H which may completely enclose a photocell andits preamplifier. K is the aperture through which light is allowed tofall on the photocell. In order to shield this apertureelectrostatically, cell F is fastened in front of it. The metallic stripB which makes 5 an electrical connection to the solution in cell F isfastened to the copper box H by means of a screw shown at L, therebygrounding the solution for electrical potentials.

.This transparent electrostatic shield may also 10 be used as a colorfilter by adding the proper coloring matter to the solution or by usingcolored glass plates. It is understood that other transparent materialsmay be substituted for the glass plates, such as fused quartz, Lucite,etc. 15

This invention should not be limited to the precise showing therein.

What is claimed is:

1. An electrostatic shield comprising a casing having at least two wallsof glass plates with go color filtering means, a conducting liquidmedium within said casing to act as an electrostatic shield throughwhich light rays may pass located between said glass plates, andterminal means for electrically connecting said conducting :5 liquidmedium to an external electrical circuit.

2. An electrostatic shield comprising a container with walls oftransparent plates, color filtering means interposed between the twooutside surfaces of said transparent plates, and a con- 30 ductingliquid medium acting as an electrostatic shield through which certaindesired light rays may pass, said conducting medium located within saidcontainer and interposed between said transparent plates. 35

3. An electrostatic shield comprising a container with Walls oftransparent plates, a conducting liquid medium having color filteringmeans, said conducting liquid medium arranged to act as an electrostaticshield through which 40 certain desired light rays may pass, saidconducting liquid located within said container and interposed betweensaid transparent plates, and terminal means for electrically connectingsaid conducting liquid to an external electrical circuit. 45

DE WITT RUGG GODDARD.

